Typically, automatic generation control (AGC) systems are designed to suspend control during emergency situations. System islanding is one such emergency situation. Conventional AGCs are specifically designed to immediately suspend control if an islanding situation is detected. An AGC attempts to detect an island by monitoring system frequency deviation and/or by comparing system frequency with the frequencies of generating units across the system. If system frequency deviates from normal, or deviates from a unit frequency, by greater than some threshold, it is an indication that, potentially, a portion of the system has been islanded and is not an integral part of the interconnection. AGC systems are typically designed to suspend control under such circumstances since AGC controlled units try to satisfy interconnected system objectives. AGC is suspended primarily to preclude dangerous and incorrect control of units. Under these conditions, some of the units may actually belong to the island so that controlling them is of no avail, in terms of meeting the interconnection obligations of the AGC function. In fact, under these circumstances, controlling islanded resources to meet the interconnection obligations of the AGC function would almost definitely result in worsening the island generation/load imbalance and island frequency deviation in a conventional system. This in turn, could result in frequency relay trips of units and loads and eventually lead to a blackout of the island in a conventional system.
Island AGC functions have been proposed that are designed to operate in parallel with the primary AGC function on-line just for the island. Such prior art systems require the operator to determine that the island exists and to identify which generators are within the island. The generators in the islanded portion are manually assigned to a second AGC function, which has the primary objective of maintaining constant frequency in the island. Thus, what is needed are improved systems, apparatus, and methods for AGC islanded operation.